Places to visit for my 9-day trip in March

I travel with my family on 19th March until 27th March to Switzerland. My trip is the next:

19th March - Genève Airport-Bern: Visit the oldtown Bern.

20th March - Bern: Visit the city. What museums do you recommend?

21st March - Bern-Luzern: Visit old town Luzern.

22nd March - Luzern - Mountain Titlis. It's too much all day?

23rd March - Luzern Rhine Fall - St Gallen - Luzern. First, do you recommend to visit the waterfalls? The other option is visit Zürich or Winterthur a few hours. What city? In other case I don't know if start the trip going to St Gallen first or at last. I'm sure to visit St Gallen with the Voralpen Express train.

24th March - Luzern - Interlaken: I'm not sure to stay in Interlaken or Grindelwald. I'll arrive at midday and I like to walk and see the mountains (no hiking).

25 th March - Interlaken - Genève by Montreaux with Golden Pass. It's necessary booking for the panoramic seats on the route Zweisimmen-Mountreaux?

the trip to the Titlis can definitely be done within one day. Our Titlis page describes the journey, the timetable allows you to search for details on this trip and other trips you have in mind;

as for March 23: your plan to first visit the Rhine Falls and then get to St. Gallen is doable. The Rhine Falls will probably not be at their best in March, but it strongly depends on seasonal weather. It's been quite mild so far, so spring may set in early and the Rhine may carry more melting water than it usually does by that time of the year. Note that the boats won't be available yet. Details are at our Rhine Falls page. You can best do the Voralpen Express on your way back from St. Gallen to Lucerne, as that allows for a direct trip without changes of trains. Alternatively you could indeed plan a city visit. I'd personally prefer Zurich, as it has lots to offer and is a bit closer to Lucerne;

Interlaken versus Grindelwald has been addressed in your previous topic;

regular Golden Pass seats don't have to be booked. In case you're looking for the special VIP seats that some Golden Pass trains have, booking is required. Please refer to www.myswissalps.com/go ldenpass/tickets for details.

Kleine Scheidegg is most famous for its splendid views of Eiger, Mönch and Jungfrau. Enjoying those views is primarily what you should do there. You can easily visit more viewing points from Grindelwald, such as First and Männlichen.

You can spend as many hours up at Kleine Scheidegg as you like. You can take short look at the views, but there are some restaurants and bars, so may also sit down, have coffee or lunch and take all the time you want. The Swiss Travel Pass allows free traveling up to Wengen/Grindelwald and indeed a 25% discount on the remaining leg to Kleine Scheidegg.

Traveling to Zermatt would be too much in your schedule. A boat trip over Lake Thun could work on March 24 (depending the rest of your plans of course).